1. Field of the Invention
The present invention relates to a method of measuring a thickness of a film contained in a laminate of multilayered structure, and more particularly, to a method of measuring by optical interferometry a thickness of a film contained in a laminate of multilayered structure comprising a polarizing film.
The present invention further relates to a method of manufacturing an eyeglass lens (polarizing lens) of multilayered structure having plural films comprising a polarizing film, and more particularly, to a method of manufacturing an eyeglass lens comprising a film of desired thickness by utilizing the above method of measuring a thickness of a film.
2. Discussion of the Background
Optical interferometry (also known as spectral ellipsometry) is widely employed to measure the thickness of individual layers contained in multilayered thin films. For example, Japanese Unexamined Patent Publication (KOKAI) Heisei No. 7-294220, which is expressly incorporated herein by reference in its entirety, proposes a method of determining the thickness of individual thin films by optical interferometry by irradiating a measurement sample in the form of a multilayered thin film with white light, dispersing the reflected light, and waveform processing the energy spectrum obtained by fast Fourier transformation of the spectrum thus obtained.
Generally, an eyeglass lens is fabricated by providing plural functional films on a lens substrate. One such functional film that is known is a polarizing film containing a dichroic dye. Eyeglass lenses comprising polarizing films are called polarizing lenses, and are employed as anti-glare glasses, for example, in industries such as the welding industry, in medical treatment, and in various sports such as skiing. Polarizing films are also employed in liquid-crystal displays and the like in addition to eyeglass lenses.
In polarizing films, the refractive index normally varies greatly with wavelength. This is because refractive index wavelength dispersion increases due to the effect of the absorption characteristics of the dichroic dye. As a result, for laminates containing polarizing films, it may be difficult to analyze the data when measuring the thickness of individual layers based on reflection spectra, and errors sometimes tend to occur in the measurement of film thickness. In some cases, it is difficult to calculate the film thickness of individual layers.
In eyeglass lenses having plural functional films, when the difference in the refractive indexes of the individual functional films is large, an interference fringe is sometimes produced, compromising optical characteristics. Thus, there are cases where it is desirable to reduce the difference in refractive indexes for visible light of the individual functional films. Accordingly, in eyeglass lenses (polarizing lenses) of multilayered structure that have been imparted with a polarizing property by providing a polarizing film on a lens substrate, for example, there are cases where the refractive index of an adjacent layer will be made close to the refractive index of the polarizing film.
On the other hand, in the measurement of film thickness by optical interferometry, the fact that various layers are distinct layers is identified and analyzed by differences in refractive index. Accordingly, when the difference between the refractive indexes of adjacent layers is small, the precision may decrease when identifying and analyzing individual layers as single layers, tending to result in measurement error. There are also cases where it becomes difficult to calculate the thickness of individual layers.